The present invention relates to a small sized (hereinafter called "miniature" or "mini") hearing aid.
More particularly, the invention relates to a miniature hearing aid having a microphone, an amplifier, a battery and a receiver, all contained in a housing.
Miniature hearing aids, especially those worn on the users head--for example, worn in or behind the ear or built into spectacle frames--have an extremely limited space for installation of the required mechanical and electrical components. Therefore, constant efforts have been directed to installing the individual components required for the conversion and amplification of sound in a most favorable and space saving manner.
A mini hearing aid of the type to which the present invention relates is disclosed in the German Utility Model Patent No. GM 7,831,808. This patent discloses a compact housing in which are packaged a microphone, an amplifier, a battery and a receiver. The electrical components of this hearing aid (transistors, resistors, capacitors, etc.), are disposed on facing sides of two printed circuit boards, arranged in parallel within the hearing aid housing. With such a packaging concept, the thickness of the circuit boards had a direct bearing on the size of the housing so that it is desirable to reduce the thickness of these circuit boards. However, too much of a reduction in the thickness of these boards leads to problems of stability and reliability. The German Patent Publication (DAS) No. 1,139,549 discloses a behind-the-ear hearing air in which the thickness of the printed circuit boards is eliminated as a factor in the external dimensions of the hearing aid. In this device, openings or recesses are provided in the circuit board into which the electrical components are countersunk. As a result, it is the thickness of the electrical components alone, rather than the thickness of these components plus the thickness of the circuit board, which determines the total constructional width of the amplifier.
With this type of circuit construction, special measures must be taken to clamp the circuit components within the recesses of the circuit board. It is known, for example from the aforementioned DAS No. 1,139,549, to provide a mechanical strap to hold the component in place. As an alternative, the British Pat. No. 1,198,449 discloses an assembly of electrical circuit components wherein the components are held in place within recesses of a circuit board either by forcing them into wedge shaped slots or by surrounding them with a small quantity of electrically insulating silicone rubber or wax.
These previously known techniques for clamping electrical components in recesses in a circuit board have certain disadvantages. The provision of a separate strap is, of course, expensive in that it requires an extra part to be manufactured and assembled. Furthermore, such a strap adds to the external dimensions of the circuit assembly. The utilization of silicone rubber, wax or some other bonding compound also adds to the cost of manufacture. The provision of wedge shaped sides in a circuit board recess is the least expensive of the clamping techniques; however, this technique can be utilized only when the component itself is tapered, cylindrical or otherwise adapted and shaped to the wedge shaped slot.